Field of the Invention
The present invention relates to a diaphragm device and an optical instrument.
Description of the Related Art
For example, in optical instruments such as digital cameras and still cameras there is provided a diaphragm device that adjusts the amount of light that passes through the lens. A diaphragm device is provided with a base plate having an aperture portion, a plurality of diaphragm blades that are supported such that they are able to open and close the aperture portion, and a drive ring that is formed so as to surround the periphery of the aperture portion and that causes the plurality of aperture blades to open or close.
The plurality of blades are supported by supporting pins, and are configured such that they are able to pivot freely around the supporting pins. A cam groove is formed in either one of the plurality of blades and the drive ring, and an engaging pin that is inserted into the cam groove is provided in the other one of the plurality of blades and the drive ring. When the drive ring is operated, this drive ring, the supporting pins, and the engaging pin work together so as to operate the plurality of blades. As a result, the aperture amount of the aperture portion in the base plate is adjusted.
Here, the supporting pins are placed in positions that correspond to the outer side in the radial direction of the drive ring, and in the axial direction of the drive ring (i.e., the thickness direction of the drive ring) (see, for example, Japanese Published Examined Application No. H7-92580), and are placed on the outer side in the radial direction of the drive ring (see, for example, PCT International Publication No. WO 2009/113363).
If the supporting pins are placed in positions that overlap with the drive ring in the axial direction, then the thickness of the entire diaphragm device is increased by the corresponding amount. Because of this, placing the supporting pins on the outer side in the radial direction of the drive ring makes it possible for the thickness of the overall diaphragm device to be reduced.
However, if the supporting pins are placed on the outer side in the radial direction of the drive ring, then although the thickness of the overall diaphragm device can be reduced, the problem arises that the size in the radial direction of the overall diaphragm device increases (i.e., when seen in plan view). Moreover, if there are restrictions on the positions of the actuator and deceleration mechanism which are used to drive the drive ring, the problem arises that the size in the radial direction of the overall diaphragm device increases even more.